This invention relates to a method for modifying the surface of a plastic material, and more particularly, to a method for modifying the surface of plastic lenses by forming a surface hard coat on the lens.
Synthetic resin lenses are used widely in the field of optics as ophthalmic lenses due to their safety, ease of manufacture and light-weight. Additionally, recent progress in flex prevention techniques and hard coating have further aided in the manufacture and wide use of synthetic resin ophthalmic lenses.
In the ophthalmic field there is strong demand for high-quality plastic lenses that have a high refractive index. A number of prior art references teach the manufacture of a high refractive index resin for use in ophthalmic lenses. These include the following Laid Open Japanese Patent Applications:
1. No. 54-41965 which teaches using a copolymer of diethyleneglycolbis(allylcarbonate) and benzylmethacrylate:
2. No. 54-77686 which teaches using a copolymer of diethyleneglycolbis(allylcarbonate) and 4-iodostyrene;
3. No. 58-15513 which teaches using a copolymer of diallylterephthalate or diallylisophthalate with a methylmethacrylate prepolymer;
4. No. 55-13747 which uses the copolymer of bisphenol A diemethacrylate and phenylmethacrylate or benzylmethacrylate; and
5. Nos. 57-54901 and 58-18602 which use a styrene monomer and a copolymer of di(metha)acrylate having a halogen substituted aromatic ring and an allyl compound or a bifunctional di(metha)acrylate.
The lens produced using the copolymers taught in the these publications are not fully satisfactory for the following reasons. For the lenses produced by the references in 1, 2 and 3 the problem arises in the process for reacting the allyl group and the (metha)acryl or vinyl group which have different rates of reactivity. The (metha)acryl group or vinyl group are fast reacting and polymerize first. The allyl group is slow reacting and polymerizes later. As a result, copolymerization does not occur. Incomplete polymerization of the allyl compound causes deterioration of heat resistance and solvent resistance the resulting lenses.
Since the (metha)acryl or vinyl compound which polymerizes first is a unifunctional monomer, these compounds are not completely polymerized or incorporated into the polymer chain. Rather, the compounds are partially extracted as a monomer which further reduces heat resistance of the resulting lens. An additional shortcoming is that the lenses manufactured in accordance with the methods taught in these publications have a refractive index lower than satisfactory.
In the method of publication 4, the reactivity of the (metha)acryl and vinyl group are similar. However, it is difficult to control the various processing conditions during manufacture of the lens. Specifically, because the (metha)acryl and vinyl groups react fast, it is difficult to control casting. Distortion occurs inside or on the lens surface which produces optical defects. Furthermore, since the vinyl and (metha)acryl groups are very sensitive to environmental conditions, it is difficult to control such conditions in addition to the polymerization conditions. Moreover, since the second monomer is unifunctional, heat resistance of the lens is reduced.
Publications Nos. 57-54901 and 58-18602 provide lenses having a high refractive index. However, the manufacturing process is extremely complex due to difficulties in controlling polymerization conditions and in completing polymerization.
In order to overcome the above deficiencies in the prior art, the resin described herein was developed. The resin has excellent chemical resistance and stable physical properties. However, it is difficult to adhere an inorganic deposition film or hard-coating layer of organic silicon, organic acryl or other similar compounds onto the surface. Generally used surface treatment methods, such as plasma treatment described in "Industrial Material" Vol. 29, No. 2, pp. 105-115 (1983), or flame treatment described in Japanese Laid Open Application No. 57-49374 are not suitable for use with the new synthetic resin lens.
Accordingly, it is desirable to provide an improved synthetic resin lens and a method for modifying the surface of the synthetic resin lens in order to form an inorganic film or hard-coating layer securely thereon.